For those of you learning Mongo and need a quick reference.
Show databases on the server
show dbs
Use a specific db on the server
use <db>
Show "tables" In Mongo, you have collections, not tables. To view the collections available:
show collections
Basic search
db.collection.find({"key": "value"})
Cursor
Your cursor is essentially the query you're using to search for something. You can set it to a variable as a shortcut as well:
var user = db.users.find(<OPTIONS>);
Search by Object ID
IDs are a bit diferent than just an ID, it is an ObjectId (ObjectId("555555555555")). ID keys will always be "_id".
db.users.find({"_id": ObjectId("55555555")})
Simple updates to one document
The structure for basic updates with .update is:
- query (find what you want to update),
- the update itself, using $set, then options.
db.users.update({"_id": ObjectId("555555")}, {$set: {"name": "Rusty"}})
**Updates for multiple documents
For updates on multiple documents, you can use {multi: true} to update multiple documents. If not defined, multi will be set to "false" (meaning Mongo will only update the first document it finds then quit).
You can also use upsert: true, which will create a document if one doesn't exist. USE THIS SPARINGLY, obviously, otherwise you may end up creating documents you don't need. Only use upsert: true if you are absolutely sure you need to create documents if one does not already exist. If not defined, upsert is set to false (meaning a new document is not created).
Example: Update all users in the users collection whose location is "Austin" and set it to "Portland". This update should apply to multiple users, but it should not create a document if one does not exist.
db.users.find({"location" {$in: "Austin"}}, {$set: "Portland"}, {multi: true})
Note we're using multi: true so this applies to all users who meet the criteria. No need to specify upsert: false since it is false by default.
Includes vs. Exists
Includes ($in) will search for documents where a certain field includes a certain value.
BE CAREFUL not to use $inc, which is increment.
You can also use a regex with your includes statement: $in: /some regex/. (Note there is a $regex operator, but it cannot be used with $in)
Exists ($exists) looks for a certain field to exist in a document. A document store is flexible, and often, some documents don't include certain fields if a document doesn't need it. Sometimes, you will want to search documents to see if a certain field exists in the document: db.users.find({"admin": {$exists: true}}).
So, $in searches for values in a field that exists, and $exists searches for the existence of a field in a document.
Other handy things
.count() will count documents matching your query.
.pretty() will output nicely formatted JSON.